KABUL (AFP) — A suicide attack near a German diplomatic convoy in Afghanistan's capital Kabul left three Afghan civilians dead Sunday as 20 other people, most of them insurgents, were reported killed in other unrest.

There was no immediate claim of responsibility for the suicide bomb, the second in Kabul in three days, but similar ones have been claimed by Taliban-led extremists waging an insurgency.

A German foreign ministry spokesman in Berlin said a vehicle belonging to its embassy in Kabul had been targeted.

"The sole occupant of the vehicle, an Afghan employee of the embassy, was injured," the spokesman said.

President Hamid Karzai's office said in a statement three civilians were killed and six wounded in the blast, which it described as a "barbaric terrorist action".

The attacker was on foot when he blew himself up in front of a boys' high school and about 200 metres (660 feet) from parliament, police said.

At least one of the dead was a municipal worker who had been cleaning the road, another worker named Waheedullah told AFP.

"I was standing here at the corner when I heard a big explosion," he said. "I went to the main road and saw one of our friends lying on roadside, covered in blood, near his wheelbarrow. His belly was badly wounded and was open.

"I saw another civilian dead nearby and I saw two civilians wounded."

It was the second suicide attack in Kabul since Thursday, when a car bomb outside the heavily barricaded US embassy killed four Afghan civilians and wounded nearly 20. The Taliban claimed responsibility for the Thursday blast.

Also Sunday, a remotely detonated bomb killed an Afghan guard for the USPI security company in the southern province of Kandahar, provincial government spokesman Zalmai Ayoubi told AFP.

Meanwhile, the US-led coalition announced it killed 17 militants on Saturday as part of its operations helping the Afghan government fight an insurgency led by the extremist Islamic Taliban, who were in government between 1996 and 2001.

Sixteen were killed in an operation against a "terrorist network" in Sarobi, about 50 kilometres (30 miles) east of Kabul in an area where 10 French soldiers were killed in an ambush in August.

The operation was against a commander of the Hizb-e-Islami faction, led by former Prime Minister Gulbuddin Hekmatyar, said to be involved in kidnappings and bomb attacks.

"As coalition forces approached the targeted buildings, 16 armed militants exited the buildings and began manoeuvring on the force.

"The militants engaged the force with small-arms fire. The force responded with small-arms fire and precision munitions and killed the militants," it said.

The US military could not confirm reports that the fighters killed Saturday were involved in the ambush on the French, the deadliest ground fighting for international soldiers since they deployed in 2001 to oust the Taliban.

Another militant was killed in an operation in the eastern province of Paktia on Saturday and 10 more were arrested, the statement said.

The man from the radical Haqqani network was believed to help move foreign militants into Afghanistan, including the Islamic Jihadist Union, which has been behind attacks in Uzbekistan.

Military officials say the insurgency in Afghanistan has drawn militants from various groups, including Al-Qaeda.

Nearly 70,000 international troops are stationed in the country to support the Afghan forces.